This invention concerns a sulfonated lignin binder. More particularly, it is related to a graft copolymer of high molecular weight sulfonated lignin material and an acrylic monomer.
As used herein, the term "lignin" has its normal connotation, and refers to the substance which is typically recovered from alkali pulping black liquors, such as are produced in the kraft, soda and other well-known alkali pulping operations. The term "sulfonated lignin", as used in this specification, refers to the product which in this specification, refers to the product which is obtained by the introduction of sulfonic acid groups into the lignin molecule, as may be accomplished by reaction of the lignin with sulfite or bisulfite compounds. As used herein, the term "lignosulfonate" refers to the reaction product of lignin which is inherently obtained during the sulfite pulping of wood, straw, corn stalks, bagasse and the like, and is a principal constituent of the spent sulfite liquor which is derived from that process. Finally, the phrase "sulfonated lignin material" encompasses both sulfonated lignin and lignosulfonate herein above described.
There are several prior art disclosures on copolymers of lignosulfonate and acrylic compounds. For example, U.S. Pat. No. 4,374,738 discloses a water-based drilling mud composition which comprises an aqueous disperson of a clay material and a graft copolymer of lignosulfonate and an acrylic compound including acrylic acid, acrylonitrile and acrylamide. In U.S. Pat. No. 4,276,077, a method is revealed for improving a soil structure by stabilization of aggregates obtained from crude lignosulfonate and a monomer selected from among acrylonitrile, vinyl acetate, acrylamide or combinations thereof. Sovient Union Patent No. 1,168,515 (July 23, 1985) teaches the use of a copolymer of lignosulfonate and (meth)acrylic acid in inhibiting the deposit of inorganic salts. A study on graft copolymerization of lignosulfonate acrylic compounds was reported in the Journal of Applied Polymer Science, Vol. 25 : 2211-2220 (1980). These cited prior art, however, failed to recognize the use of a copolymer of lignosulfonate and an acrylic compound as a binder, and further failed to disclose or recognize a critical parameter (high molecular weight of sulfonated lignin materials) necessary for making an effective lignin binder.
Crude lignosulfonates as employed in the prior art generally do not have high enough molecular weights for making the effective binder of the present invention. The % by weight of said crude lignosulfonates in excess of 5,000 daltons are approximately:
Softwood Lignosulfonates--30% PA0 Hardwood Lignosulfonates 15%
A major object of this invention is to provide an effective lignin binder. Another object of this invention is to provide a binder from sulfonated lignin materials.
An additional object of this invention is to provide a simple process for the production of the sulfonated lignin binder.
Other objects and features of this invention may be evident in the following detailed disclosure.